By tracking your heart rate during the training, you will be able to know how intense your workout is. Thanks to that, Endomondo will also count more accurately how much calories you have burned.
Heart rate zones are a great tool for monitoring the intensity of your workouts. You can train smarter with HR monitor. For example by staying in the "fat burn" heart rate zone you can burn up to 85% energy from fat. Find out how much time you spend in the five different HR zones.
Swimmo uses Bluetooth to be compatible heart rate monitor for Endomondo. It is a universal and open protocol. Unlike ANT+ proprietary protocol used by other straps, Swimmo works together with many other fitness apps of your choice. This way you won't be locked in.